U.S. patent number 6,602,271 [Application Number 09/735,140] was granted by the patent office on 2003-08-05 for collapsible blood filter with optimal braid geometry.
This patent grant is currently assigned to Medtronic Ave, Inc.. Invention is credited to Bruce Adams, Jerry R. Brightbill, David S. Brin, Dennis L. Brooks, Nareak Douk, Robert D. Lashinski, Ahmed Malek, Nasser Rafiee.
United States Patent |
6,602,271 |
Adams , et al. |
August 5, 2003 |
Collapsible blood filter with optimal braid geometry
Abstract
The present invention is a collapsible blood filter for use
during a vascular procedure, such as angioplasty or stent
deployment. A filter made of braided filaments is located on the
distal end of a delivery member, and the filter is deployed
downstream of the vascular treatment site to capture emboli
released during and immediately after the procedure. Optimal braid
geometry of the filter ensures that captured emboli will be
retained during collapse and removal of the filter following the
procedure.
Inventors: |
Adams; Bruce (Malden, MA),
Malek; Ahmed (Cairo, EG), Brightbill; Jerry R.
(Newton, MA), Rafiee; Nasser (Andover, MA), Douk;
Nareak (Lowell, MA), Brin; David S. (Danvers, MA),
Brooks; Dennis L. (Windsor, CA), Lashinski; Robert D.
(Sebastopol, CA) |
Assignee: |
Medtronic Ave, Inc. (Santa
Rosa, CA)
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Family
ID: |
24954534 |
Appl.
No.: |
09/735,140 |
Filed: |
December 12, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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578244 |
May 24, 2000 |
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Current U.S.
Class: |
606/200;
606/191 |
Current CPC
Class: |
A61F
2/013 (20130101); A61F 2230/008 (20130101); A61F
2002/018 (20130101); A61F 2230/0006 (20130101); A61F
2230/0067 (20130101); A61F 2002/015 (20130101) |
Current International
Class: |
A61F
2/01 (20060101); A61F 2/00 (20060101); A61M
029/00 () |
Field of
Search: |
;606/200,191,194,195,198,199 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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96/01591 |
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Jan 1996 |
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WO |
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98/33443 |
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Aug 1998 |
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WO |
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99/16382 |
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Apr 1999 |
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WO |
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99/22673 |
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May 1999 |
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WO |
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99/23976 |
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May 1999 |
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WO |
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WO/99/23976 |
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May 1999 |
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WO |
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00/44308 |
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Aug 2000 |
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WO |
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01/05329 |
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Jan 2001 |
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WO |
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01/08595 |
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Feb 2001 |
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WO |
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01/15929 |
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Mar 2001 |
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WO |
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01/21100 |
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Mar 2001 |
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WO |
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02/05729 |
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Jan 2002 |
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WO |
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Primary Examiner: Hale; Gloria M.
Attorney, Agent or Firm: Medtronic Ave, Inc.
Parent Case Text
This application is a continuation-in-part of U.S. patent
application Ser. No. 09/578,244 entitled "Distal Protection Device"
and filed May 24, 2000, the contents of which are hereby
incorporated by reference.
Claims
We claim:
1. A collapsible blood filter for capturing emboli during an
endovascular procedure at a treatment site, the filter comprising a
tube formed by braided filaments that define pores, the filter
having at least one inlet opening that is substantially larger than
the pores, the filter having an axis and tapered ends, wherein
relative movement of the ends along the axis accompanies
transformation of the filter between a collapsed configuration and
a deployed configuration, and wherein the pore-defining filaments
of the braided tube form a maximum included angle of about 90
degrees, as measured across the axis when the filter is in the
deployed configuration.
2. The blood filter of claim 1 wherein at least a portion of the
filter between the ends is cylindrical in shape when the filter is
in the deployed configuration.
3. The blood filter of claim 1 wherein the shape of the deployed
configuration is ovoid.
4. The blood filter of claim 1 wherein the deployed configuration
is sized to fill a selected cross-sectional area distal to the
treatment site.
5. The blood filter of claim 1 wherein at least one of the braid
filaments is a wire comprising radiopaque metal.
6. A distal protection device for capturing emboli during an
endovascular procedure at a treatment site, the device comprising:
a delivery member having a proximal end and a distal end; and a
collapsible filter adjacent the distal end of the delivery member,
the filter comprising a tube formed by braided filaments that
define pores, the filter having at least one inlet opening that is
substantially larger than the pores, the filter having an axis and
tapered ends, wherein relative movement of the ends along the axis
accompanies transformation of the filter between a collapsed
configuration and a deployed configuration, and wherein the
pore-defining filaments of the braided tube form a maximum included
angle of about 90 degrees, as measured across the axis when the
filter is in the deployed configuration.
7. The distal protection device of claim 6 further comprising: a
sheath being slidingly moveable over at least part of the filter
for transforming the filter between the deployed configuration and
the collapsed configuration.
8. The distal protection device of claim 6 wherein the deployed
configuration is sized to fill a selected cross-sectional area
distal to the treatment site.
9. The distal protection device of claim 6 wherein at least one of
the braid filaments is a wire comprising radiopaque metal.
10. A system for treating a vascular stenosis, comprising: an
elongate delivery member having proximal and distal ends; a
collapsible filter mounted adjacent the distal end of the delivery
member, the filter having a tube formed by braided filaments that
define pores, the filter having at least one inlet opening that is
substantially larger than the pores, the filter having an axis and
tapered ends, wherein relative movement of the ends along the axis
accompanies a transformation of the filter between a collapsed
configuration and a deployed configuration, and wherein the
pore-defining filaments of the braided tube form a maximum included
angle of about 90 degrees, as measured across the axis when the
filter is in the deployed configuration; and a vascular treatment
catheter capable of being slidably disposed about the delivery
member.
11. A system according to claim 10 further comprising a sheath
capable of being slidably disposed about the delivery member and
extendable over at least a proximal portion of the filter when the
filter is in the collapsed configuration.
12. A system according to claim 10, wherein the vascular treatment
catheter is a balloon angioplasty catheter.
13. A system according to claim 10, wherein the vascular treatment
catheter is a stent delivery catheter.
14. A method of making a collapsible blood filter, the method
comprising: braiding wire-like filaments to form a tubular filter
having pores therein, the filter having an axis, a deployed
diameter and two ends, the filaments intersecting at a maximum
angle of about 90 degrees, as measured across the axis when the
filter is at the deployed diameter; forming tapered ends on the
filter by drawing the ends to a second diameter that is
significantly smaller than the deployed diameter; and heat treating
the filter to fix a selected shape thereof.
15. The method of making a blood filter according to claim 14,
further comprising: forming at least one inlet opening in a tapered
end of the filter, the opening having a selected size and shape
that is substantially larger than the pores by forcing a mandrel of
the selected size and shape into a pore formed by the braided
filaments.
16. The method of making a blood filter according to claim 14,
wherein the braiding step further includes braiding a distal
portion of the filter body more tightly than the remainder of the
body.
17. The method of making a blood filter according to claim 14,
wherein the wire-like filaments comprise shape-memory metal
wires.
18. The method of making a blood filter according to claim 14,
wherein at least one of the wire-like filaments is a wire
comprising radiopaque metal.
Description
FIELD OF THE INVENTION
The present invention relates generally to endovascular devices for
capturing particulate. More particularly, the invention relates to
a filter assembly located at the distal end of a delivery member to
capture emboli in a blood vessel during a vascular procedure and
then remove the captured emboli from the patient after completion
of the procedure.
BACKGROUND OF THE INVENTION
A variety of treatments exists for dilating or removing
athersclerotic plaque in blood vessels. The use of an angioplasty
balloon catheter is common in the art as a minimally invasive
treatment to enlarge a stenotic or diseased blood vessel. This
treatment is known as percutaneous transluminal angioplasty, or
PTA. To provide radial support to the treated vessel in order to
prolong the positive effects of PTA, a stent may be implanted in
conjunction with the procedure.
Thrombectomy is a minimally invasive technique for removal of an
entire thrombosis or a sufficient portion of the thrombosis to
enlarge the stenotic or diseased blood vessel may be accomplished
instead of a PTA procedure. Atherectomy is another well known
minimally invasive procedure that mechanically cuts or abrades a
stenosis within the diseased portion of the vessel. Alternatively,
ablation therapies use laser or RF signals to superheat or vaporize
the thrombis within the vessel. Emboli loosened during such
procedures may be removed from the patient through the
catheter.
During each of these procedures, there is a risk that emboli
dislodged by the procedure will migrate through the circulatory
system and cause clots or strokes. Thus, practitioners have
approached prevention of escaped emboli through use of occlusion
devices, filters, lysing and aspiration techniques. In atherectomy
procedures, it is common to remove the cut or abraded material by
suction though an aspiration lumen in the catheter or by capturing
emboli in a filter or occlusion device positioned distal of the
treatment area.
Prior art temporary filters or occlusion devices are associated
with either a catheter or guidewire and are positioned distal of
the area to be treated. One prior art collapsible filter device
includes a filter deployed by a balloon distal of a dilatation
balloon on the distal end of a catheter. The filter consists of a
filter material secured to resilient ribs. The ribs are mounted at
the distal end of the catheter. A filter balloon is located between
the catheter exterior and the ribs. Inflation of the filter balloon
extends the ribs outward across the vessel to form a trap for
fragments loosened by the dilatation balloon. When the filter
balloon is deflated, the resilient ribs retract against the
catheter to retain the fragments during withdrawal of the
catheter.
Another prior art filter arrangement includes several filter
elements fastened in spaced apart arrangement along the length of a
flexible elongate member. This forms an open-mouthed tubular
sock-like arrangement to capture the emboli within. The filter is
collapsed around the flexible elongate member by wrapping it
spirally.
Yet another prior art filter includes a filter mounted on the
distal portion of a hollow guidewire or tube. A core wire is used
to open and close the filter. The filter has an expandable rim at
its proximal end formed by the core wire. The filter is secured at
the distal end to the guide wire.
Another prior art device has a filter made from a shape memory
material. The device is deployed by moving the proximal end of the
filter towards the distal end. It is collapsed and withdrawn by
sliding a sheath over the filter and then removing the sheath and
filter together.
A further prior art filter device discloses a compressible
polymeric foam filter mounted on a shaft that is inserted over a
guidewire. The filter is inserted collapsed within a housing which
is removed to deploy the filter once in position. The filter is
retracted by inserting a large bore catheter over the shaft and the
filter, and then removing the shaft, filter and catheter
together.
Another prior art filter arrangement has a filter comprised of a
distal filter material secured to a proximal framework. This filter
is deployed in an umbrella manner with a proximal member sliding
along the shaft distally to open the filter and proximally to
retract the filter. A large separate filter sheath can be inserted
onto the shaft and the filter is withdrawn into the sheath for
removal from the patient.
Other known prior art filters are secured to the distal end of a
guidewire with a tubular shaft. Stoppers are placed on the
guidewire proximal and distal of the filter, allowing the filter to
move axially and retract independently of the guidewire. A sheath
is used to deploy and compress the filter.
A problem associated with known temporary filter arrangements is
that emboli may not be fully contained within the filter. Emboli
can build up in the area just proximal of the filter, including any
frame portion proximal of the filter assembly. As the filter is
closed, emboli not fully contained in the filter can escape around
the filter into the circulatory system and cause potentially life
threatening strokes.
Another known prior art collapsible filter is formed from braided
filaments. The pores thus created change in size and shape as the
filter expands during deployment or as the filter collapses for
removal. However, there are previously unrecognized problems
associated with the changing of pore sizes during use of a braided
filter. Depending on the braid geometry of the filter, the pore
size may increase during the transition of the filter from the
expanded, or deployed size to a smaller size required for removal
of the filter from the body. This problem is critical during
retrieval of the filter when an increase in pore size may allow the
escape of embolic material previously captured by the filter.
Therefore, what is needed is a filter arrangement that addresses
the problem of emboli not fully contained in the filter assembly.
Furthermore, there is a need for a filter assembly that is
adaptable for delivery with standard PTCA balloon or stent delivery
catheters. Additionally there is a need for a filter arrangement
that is secure by being mounted at its distal and proximal ends to
the delivery member ensuring proper placement of the filter
throughout deployment, capture of the emboli and subsequent removal
of the filter and captured emboli. There is also a need for a
braided filter with optimal braid geometry to ensure that the pores
of the filter do not become larger during removal, when the filter
transitions between a deployed size and a collapsed size.
SUMMARY OF THE INVENTION
The present invention is a distal protection device for use in
vascular procedures. The distal protection device includes a filter
assembly adjacent the distal end of a delivery member used in the
procedure. The proximal and distal ends of the filter assembly are
fixed to the delivery member such that the ends cannot move
longitudinally along the delivery member, but may rotate
independently of the delivery member core. The filter assembly
includes an expandible frame with a distal portion acting as the
emboli filter. The emboli filter is sized sufficiently to expand
and cover the cross sectional area of the vessel distal of the
intended treatment area.
The filter assembly may have a variety of configurations. In one
embodiment, the frame consists only of the proximal portion of the
filter assembly, with the distal half formed from filter material.
The frame can have a braided configuration or consist of a
sinusoidal ring element adjacent the filter material with helical
segments extending from the sinusoidal ring to the delivery member.
In another embodiment, the frame forms a basket arrangement and
includes the filter material in the distal half of the basket. Such
a frame can be configured with a tighter braid on the distal end,
thus obviating the need for a separate filter material. This
embodiment may have a generally ovoid shape.
The filter assembly further includes a moveable sheath for
positioning the emboli filter between an expanded position and a
collapsed position. The sheath extends over the frame, collapsing
the frame and filter of the assembly as they are drawn into the
sheath. Likewise, when the frame and filter are removed from the
sheath, they will expand so that the filter will cover the cross
sectional area of the vessel distal of the treatment area.
Alternative embodiments of the filter assembly can include an
aspiration lumen and/or a flushing lumen extending through the
sheath. This allows large emboli to be lysed or aspirated prior to
retracting the filter and removing it from the patient.
Another alternative embodiment of the filter assembly has the
proximal end of the filter longitudinally fixed to the delivery
member, the distal end of the filter being slidingly attached to
the member. When a sheath is passed over the filter to compress it
for delivery or retrieval, the distal end of the filter slides
distally on the delivery member, extending the length of the
filter. The filter of this embodiment may also include a frame that
is densely braided to form a basket with fine pores. The filter
also has large inlet openings that are formed in the proximal end.
The deployed shape of this filter embodiment is generally that of a
teardrop, the proximal end having a generally obtuse cone and the
distal end having a generally acute cone. A cylindrical well
defines the filter body between the proximal and distal cones.
For embodiments that utilize tightly braided frame elements to form
the filter medium, the braid geometry is optimized such that the
pores only get smaller in size as the filter is collapsed for
retraction. In this way, emboli that have been trapped in the
braided filter during an endovascular procedure will not escape
through the filter orifices as they change shape during the filter
withdrawal procedure.
The sheath is configured to be used with either a rapid exchange
arrangement or an over-the-wire arrangement as is well known to
those skilled in the art.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a side view of a catheter and delivery member
incorporating a distal protection device of the present invention,
with the distal protection device shown deployed in a vessel;
FIG. 2 is a side view taken of the distal portion of a catheter and
delivery member incorporating a distal protection device of the
present invention, with the distal protection device shown
constrained in the catheter, which is shown in section;
FIG. 3 is a side view of a second filter arrangement of the present
invention, shown deployed;
FIG. 4 is a side view of a third filter arrangement of the present
invention, shown deployed;
FIG. 5 is a side view of a rapid exchange styled delivery sheath
and a fourth filter arrangement of the present invention;
FIG. 6 is a side view of a fifth filter arrangement of the present
invention;
FIG. 7 is view of the inlet end of the fifth filter arrangement
shown in FIG. 6;
FIG. 8A is an enlarged view of a section of braid material utilized
in a blood filter of the prior art;
FIG. 8B shows two graphs depicting corresponding changes in pore
size and braid angle as the prior art braid of FIG. 8A changes in
diameter;
FIG. 9A is an enlarged view of a section of braid material utilized
in a blood filter of the present invention;
FIG. 9B shows two graphs depicting corresponding changes in pore
size and braid angle as the braid of FIG. 9A changes in
diameter;
FIG. 10 is a flow chart depicting the method of making the fifth
filter arrangement shown in FIG. 6.
The figures are not necessarily to scale.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is a distal protection device, designated 10
in FIG. 1 for use in minimally invasive procedures, such as
vascular procedures or other procedures where the practitioner
desires to capture material that may be dislodged during the
procedure. Distal protection device 10 includes filter assembly 12
located adjacent distal end 14 of delivery member 16. In this
preferred embodiment delivery member 16 can be a modified guidewire
assembly, hereinafter referred to as either "delivery member,"
"guidewire," or "core wire." Filter assembly 12 is delivered,
deployed and retrieved by sheath 18, which is slidable over filter
assembly 12. When distal protection device 10 is in a constrained
position, filter assembly 12 is collapsed within sheath 18 as shown
in FIG. 2. When filter assembly 12 is deployed, sheath 18 is
withdrawn, releasing filter assembly 12 as shown in FIG. 1.
Filter assembly 12 includes filter 20 and frame 22 and is secured
to delivery member 16 at distal filter portion 24 and proximal
filter portion 26. Preferably, filter assembly ends 24 and 26 are
fixed in the longitudinal position, but are capable of rotational
movement independent of guidewire core 17 while maintaining the
longitudinal position. Filter 20 is formed from a suitable mesh or
porous material that will filter emboli from blood while permitting
sufficient perfusion therethrough. For example, a porous filter can
be formed from urethane material by adding salt, sugar or other
granular particles during the casting of the urethane filter.
Following the cutting and curing processes, these granular
particles are dissolved forming a porous urethane filter as is well
known to those skilled in the art. Other suitable filter materials
may include ePTFE or other Teflon.RTM. fluoropolymers by DuPont de
Nemours in Wilmington, Del., Kevlar.RTM. para-aramid, also by
DuPont, or nylon and the like having an appropriate porous
construction to filter emboli from blood passing through the
filter.
Filter assembly 12 is positioned concentric with delivery member
16. Filter 20 is sized such that when it is fully deployed, as in
FIG. 1, filter proximal edge 28 will contact the inner surface of
blood vessel wall 30. The surface contact is preferably maintained
over the entire cross section to prevent any emboli from escaping
past filter 20. Filter 20 is preferably secured at proximal filter
edge 28 to frame 22 and at distal filter portion 32 to the delivery
member 16.
Frame 22 of filter assembly 12 is an expandable frame made from a
shape memory material such as nitinol, stainless steel, a suitable
polymer or other suitable materials. Several struts, designated
generally as 34, extend from a connection with delivery member 16
at proximal filter portion 26 to proximal edge 28 of filter 20, to
form frame 22, as seen in FIGS. 1 and 2.
Alternatively, struts 38 may extend around filter 40 forming basket
frame 42 with filter 40 on at least distal portion 44 of basket
frame 42 as shown in FIG. 3. In such an arrangement, basket frame
42 is secured preferably at proximal and distal ends 46, 48
respectively to guidewire 50. As with the embodiment of FIG. 1,
basket frame 42 is fixed on the guidewire at a longitudinal
position where it is capable of rotational movement independent of
guidewire 50. Filter 40 is secured at its proximal and distal ends
52, 54 to basket frame 42. Filter 40 can be secured to struts 38 on
the distal portion 44 of basket frame 42. Alternatively, filter 40
may be formed on basket frame 42 by dip coating select portions of
basket frame 42 with a suitable material such as urethane and
treating the material to form the desired porous structure on
distal portion 44.
A variety of strut configurations are suitable including the braid
configuration shown in FIG. 1. Struts 56 of filter assembly basket
58 shown in FIG. 4 have a dense braid on distal portion 61 that
transitions to a less dense braid on proximal portion 63. Filter
material may be located on distal portion 61 either by having a
separate filter material or by dip coating selected portions of the
basket 58 as discussed above with respect to the embodiment shown
in FIG. 3. Alternatively, struts 56 may act as braid filaments, the
braid being sufficiently dense on distal portion 61 to act as a
filter, thus obviating the need for separate filter material or
selective dip coating of basket 58. As mentioned with respect to
expandable frame 22 in FIG. 1, braid filaments may be made of
shape-memory metal, such as nitinol, stainless steel, or of
non-metallic materials that are sufficiently resilient to provide a
self-supporting filter assembly. To enhance visualization of the
braided filter under fluoroscopy, at least one of the filaments may
be a wire that is made of, or plated with, a radiopaque metal such
as gold, platinum, tungsten or alloys thereof. Filter assembly
basket 58 is fixed to the guidewire 65 at its proximal and distal
filter ends 66, 68. Again, filter assembly basket 58 is preferably
fixed at a longitudinal position on guidewire 65 where it is
capable of rotational movement independent of the guidewire core.
Sheath 70 is used to deploy filter assembly basket 58.
Filter assembly 80 shown in FIG. 5 is similar to the filter
arrangement of FIG. 1. Frame 82 consists of distal ring 84 formed
from a sinusoidal element. Extending from ring 84 to guide wire 86
are helical members 90. For example, one such member 90 extends
between apex 88 of ring 84 and guidewire 86. Distal end 96 of
filter 92 is secured to guidewire 86.
Sheath 98 includes aspiration lumen 100 and lysing lumen 102. While
two lumens are shown, as known to those skilled in the art, either
lumen 100 or lumen 102 alone may be incorporated in sheath 98.
Sheath 98 also includes a short guidewire lumen 104 providing a
sheath configured as a rapid exchange sheath.
FIG. 6 shows a fifth filter arrangement surrounding a body forming
mandrel. This filter embodiment may be used in the previously
described filter assemblies, especially that of FIG. 4. Filter 220
is shaped to have cylindrical central well 232, distal cone 234,
proximal surface 230, and proximal and distal ends 266 and 268,
respectively. Either sheath 18 or sheath 98 can be used to
transform filter 220 between its generally teardrop shaped,
deployed configuration shown in FIG. 6 and a collapsed
configuration similar to that of filter assembly 12, shown in FIG.
2.
The cylindrical shape of central well 232 provides greater surface
area for contacting the vessel wall. With greater contact area,
filter 220 will have more secure apposition against the vessel wall
during treatment. Cylindrical well 232 can also provide a larger
inner volume for collection of emboli. Rounded shoulder 231 forms
the transition from surface 230 to cylindrical central well 232. As
viewed from the proximal end, four inlet ports 290 are equally
spaced around proximal surface 230, each port having an axis 292
in-plane with a radius of the central well 232. The included cone
angle .alpha. of proximal surface 230 is preferably more than
90.degree., most preferably about 100.degree.. The combination of
cone angle .alpha. and rounded shoulder 231 has shown a reduced
likelihood of scraping the vessel wall and an improved particulate
collection efficiency.
Filter 220 is similar to filter assembly basket 58 shown in FIG. 4,
wherein the struts 56 alone make the filter basket by using a
densely braided structure. Filter 220 is formed with a generally
constant pitch braid, preferably providing a uniform pore size of
approximately 75-125 microns, such that no additional filter
material is necessary. As depicted schematically in FIG. 10, filter
220 is made from a continuous braided tube, which is cut into
sections to form individual filter bodies. Filter 220 is tapered at
the ends, preferably by drawing filter ends 266, 268 over body
forming mandrel 200. While filter ends 266, 268 are held in
position, filter 220 is heat treated at a time and temperature
suitable for the selected braid filament material, as is well known
to those of skill in the art. Inlet ports, or openings 290 are
formed by inserting port forming mandrels, not shown, through pores
in surface 230 and into mandrel retaining holes 210 in body forming
mandrel 200. Preferably, a second heat treatment is applied to the
braid of filter 220, after which all mandrels are removed and
filter 220 recovers to its heat set shape. Optionally, a single
heat treatment can be used to form both filter 220 and ports
290.
Ports 290 are best described when viewed from the proximal end of
the filter 220 because this view shows the shapes of the mandrels
used to make inlet ports 290. Ports 290 provide filter inlet
openings that are substantially larger than the size of the pores
in filter 220. Ports 290 may have a variety of preferably rounded,
symmetrical shapes, each having an axis 292 in-plane with a radius
of the cylindrical central well 232. To efficiently gather
particulate matter, ports 290 should also expose as much of the
proximal surface 230 as possible, especially near its perimeter,
without compromising the structural integrity of filter 220. Such
ports 290 will have axes 292 as long as possible, such as
approximately 90% of the difference between the radius of central
well 232 and the radius of proximal end 266.
FIG. 8A shows a section of braided distal portion 61' of prior art
blood filters and FIG. 8B shows the concomitant problem solved by
the current invention. In FIG. 8A, braid filaments 56' form a fully
deployed tubular filter body having axis 57'. Braid angle .theta.'
is formed between braid filaments 56', and is measured across axis
57'. Pore size 5' depicts the size of a spherical particle that can
pass through the orifices formed in braided distal portion 61'. In
braided tubular structures, such as filters, changes in diameter
are accompanied not only by changes in length, but more importantly
by changes in the dimensions of the rhombus-shaped orifices formed
between braid filaments. For example, lengthening the tubular
filter will cause lengthening of the orifice in the direction
parallel to the axis of the body, and synchronous shortening of the
orifice in the circumferential direction. When such lengthening
begins, if the orifice is shorter in the axial direction than in
the circumferential direction, then the cross-sectional area, and
especially the pore size of the orifice will increase until the
orifice becomes square. In the prior art embodiment of FIG. 8A,
angle .theta.' is greater than a critical angle of 90.degree., such
that pore size 5' will actually increase during collapse of the
filter until the filter diameter reaches a point where angle
.theta.' passes through the critical angle. Emboli that have been
trapped in the braided filter during an endovascular procedure may
escape through the filter orifices as these filter orifices grow in
size during collapse and withdrawal of the filter. After the
orifices reach a maximum size, when angle .theta.' is at the
critical angle, the orifices will begin shrinking as the filter
continues to collapse. FIG. 8B shows this undesirable change in
pore size in prior art Example 1 which has the following
properties.
Example 1 Wire thickness 0.002 in. Pics/in. 100 Number of wire
carriers 48 Braid diameter 0.25 in Braid angle, across axis
146.degree.
In accordance with the invention, the optimal braid geometry for
collapsible blood filters has been found to include an inter
filament braid angle of not more than 90.degree., as measured
across the axis. Example 2 is a collapsible blood filter having
this optimal geometry and having been braided in conformance with
the following parameters.
Example 2 Wire thickness 0.002 in. Pics/in. 92 Number of wire
carriers 144 Braid diameter 0.25 in Braid angle, across axis
90.degree.
FIG. 9A shows a section of braided distal portion 61 of Example 2.
Braid filaments 56 form a fully deployed tubular filter body having
axis 57. Braid angle .theta. is formed between braid filaments 56,
and is measured across axis 57. FIG. 9B shows that, as the braid of
Example 2 is collapsed in diameter, pore size 5 only becomes
smaller, ensuring that any captured embolic material will remain
inside the filter during withdrawal of the device from the
patient.
The deployment of filter assembly 12 will now be described,
although the procedure explained is equally applicable to any of
the filter assembly embodiments disclosed herein. The deployment
mechanism includes sheath 18 that is sized to travel over delivery
member 16 and receive the filter assembly 12 therein as shown in
FIG. 2. Sheath 18 may incorporate an aspiration lumen 60.
Additionally, sheath 18 may incorporate a flushing lumen 62 (FIG.
1) to enable the practitioner to flush the filter assembly with a
lysing agent prior to and during the procedure to remove emboli
lodged on the struts. The sheath is constructed for use as either
an over-the-wire system shown with sheath 18 in FIG. 1, or a rapid
exchange system, shown with sheath 98 in FIG. 5.
In operation, sheath 18 is extended over delivery member 16 until
it fully covers filter assembly 12 as shown in FIG. 2. Sheath 18,
filter assembly 12 and delivery member 16 are then inserted into
the patient and routed to the area to be treated, designated as 64
in FIG. 1. Filter assembly 12 and sheath 18 are positioned past, or
downstream of the area 64 to be treated. Sheath 18 is then
withdrawn, releasing struts 34 of filter assembly 12. As struts 34
resume their unrestrained position, filter 20 expands to fill the
cross sectional area of the vessel. Sheath 18 may then be
completely withdrawn from delivery member 16 and then an
appropriate second device, such as a treatment catheter, can be
routed over delivery member 16 to the treatment area.
During and after the treatment such as, an angioplasty, atherectomy
or the like procedure, emboli can be dislodged. The emboli will
travel downstream and be captured by filter 20. The treatment
catheter is removed after the procedure and sheath 18 is reloaded
on delivery member 16 and is advanced to treatment area 64. Prior
to collapsing the filter assembly 12, the practitioner can aspirate
the area to remove any loose emboli that may not be sufficiently
captured in filter 20. For example, emboli may be lodged on struts
34 proximal of filter 20. When filter 20 is collapsed, these
uncollected emboli may escape into the blood stream. Thus, the
particles should be removed. Furthermore, the practitioner may
choose to flush the area with a lysing agent to reduce the size of
the emboli within filter 20 or struts 34 prior to removing the
filter.
The practitioner then extends sheath 18 over filter assembly 12
compressing filter 20 and the captured emboli within sheath 18. If
filter 20 incorporates filter material that has been braided with
optimal geometry as described above, then the pores of the filter
will only become smaller during compression of filter 20, and no
captured embolic material will escape therethrough. Finally, sheath
18, filter assembly 12 and delivery member 16 can be removed from
the patient.
The foregoing embodiments and examples are illustrative and are in
no way intended to limit the scope of the claims set forth herein.
The filter can be mounted onto a delivery member such as a catheter
or integrally with a dilatation balloon for advancing across a
tight stenosis. The braid designs are shown in one-over-one
configuration, but two-over-two or other configurations are also
applicable, as is well known to those of skill in the art. These
and other alternatives are within the scope of the invention.
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